Experiments on vented hydrogen-air deflagrations: The influence of hydrogen concentration

The explosion venting of hydrogen-air mixtures with equivalence ratios ranging from 0.4 to 6.0 was investigated in a small vented cylindrical vessel. The experimental results show that the maximum internal overpressure initially increases with an increase in hydrogen equivalence ratio up to approximately 1.6 and subsequently decreases. The discrepancy between the maximum internal overpressure and the vent burst pressure is significantly high for equivalence ratios ranging from 1.0 to 2.0 but low for very lean or very rich mixtures. Buoyancy has a significant effect on the evolution of the internal flame bubble for very lean hydrogen-air mixtures only. The speed of the external flame oscillates violently and its maximum value is achieved at a distance downstream from the vent. The maximum length of the flame ejected from the vent, which depends on the hydrogen equivalence ratio, may be underestimated by engineering models.